2) Control Systems in the Sugar Refining Process

The process units shown in Fig. B-4 form part of a process to refine sugar. Raw sugar is fed to the process through a screw conveyor. Water is sprayed over it to form a sugar syrup. The syrup is heated in the dilution tank. From the dilution tank the syrup flows to the preparation tank, where more heating and mixing are accomplished. From the preparation tank the syrup flows to the blending tank. Phosphoric acid is added to the syrup as it flows to the blending tank. In the blending tank lime is added. This treatment with acid, lime, and heat serves two purposes. The first is that of clarification; that is, the treatment causes the coagulation and precipitation of the no-sugar organics. The second purpose is to eliminate the coloration of the raw sugar. From the blending tank the syrup continues to the process.

A. The following variables are thought to be important to control:

1. Temperature in the dilution tank.

2. Temperature in the preparation tank.

3. Density of the syrup leaving the preparation tank.

4. Level in the preparation tank.

5. Level in the 50% acid tank. The level in the 75% acid tank can be assumed constant.

6. The strength of the 50% acid. The strength of the 75% acid can be assumed constant.

9. Temperature in the blending tank.

10. The blending tank requires only a high-level alarm.

Design the control systems necessary to control all of these variables. Describe the action of control valves and controllers.

B. How would you control the production rate?